You are comparing significantly different wheels. BBS is a contract manufacturer for BMW wheels along with their own line of aftermarket wheels. The RGR model you referred to is a cold forged heat treated wheel of exceptional strength. Many race teams use the RGR wheels on their track cars. I'm not familiar with the other brand you mentioned but I suspect a bit of research will show they are gravity cast or low-pressure cast which is much less expensive a manufacturing method than forging.
No matter what brand you go with make sure to get hub-centric wheels or your car will have a perpetual vibration caused by wheels that are not quite centered on the spindle. It is a well know problem for wheels that are of generic design that rely on the wheel lugs to center the wheel.
Good luck
RJD